Twin-wheel caster



Nov. 28, 1933. R J, MLSON 1,936,701

TWIN WHEEL CASTER Filed June 21, 1932 Z'Sheets-Sheet l INVENTOR fRobzgt QJJWiISOn MW *M ATTORNEYS NOV. 28, 1933. R J w so 1,936,701

TWIN WHEEL CASTER Filed June 21, 1932 2 Sheets-Sheet 2 h s 11",! 3/ L- INVENTOR {12019613 21. \V'EISOh M W ATTORNEYS Patented Nov. 28, 1933 p UNITED STATES PATENT; OFFICE TWIN-WHEEL I CASTER Robert J. Wilson, Seattle, Wash. Application June 21,1932. Serial No. 618,545 4 Claims. (o1. 1647) My present invention relates to the art of ent from the following description taken in casters and more particularly to an improvement connection with the accompanying drawings, in a twin wheel caster. wherein Many forms of casters have been produced in Figure 1 is a front elevation View of my device.

the past, all with their particular features. In Figure 2 is a side elevation of my caster, the my present caster arrangement I provide two base of which is in section and showing one of caster wheels which are so disposed as to abut the caster wheels removed to more clearly show one another at their lowermost point so that the interior construction. p in effect the caster bears on about the same floor Figure 3 is a side elevation of my complete 1. space as a single wider caster wheel. caster unit.

Nowit is well known that a single wheel cast- Figure 4 is a cross sectional view in elevation er is desirable over a two wheel caster of usual along the line .4 of Figure 2. construction in that any obstructions which may Figure 5 is a perspective view showing one be present will be ridden over whereas in the two manner in which my casters are used.

15 wheel caster construction it the obstruction is Figure 6 is top plan view of my caster taken to slue the caster around so that it tends to drag portion only in section. sideways and this results in increased friction, Figure '7 is a plan sectional View taken along erratic movement of the supported device and the line 7--7 of Figure l.

in front of only one of the two wheels it tends along the line 66 of Figure 3 showing one often results in many breakages of the caster, Figure 8 is a vertical sectional View taken 7;;

scratched floors and the like. The objection of along the line 83 of Figure 3. V 7 that type of caster, that is'the single wheel caster, Referring to the drawings, throughout which is that a yoke must be provided which extends like reference characters indicate likeparts, 10 around to each side of the hub. This makes it designates the supporting frame or base of my 1 impossible to employ a large caster wheel, as could caster. This may have any marginal outline but so be employed in the two caster wheel arrangement. it is desirable that it be of minimum thickness; My present device makes it possible to employ either secured to frame 10 or formed as an intecaster wheels of the greatest possible diameter gral part thereof is the swivel pin 12. The long and at the same time equally support the load so pin shown gives the maximum mechanical ad- 0 that there are no unusual strains or stresses vantage against any overturning moment- This upon the casters themselves. A further -advan- I prefer to arrange as slightly coned having its tage of my present construction resides in having greatest diameter at the point where it joins the two casterwheels disposed at a slight angle base 16. Pivotally disposed onpin 12 is the axle to each other, that is the axle is bent downwardsupporting frame lei. This I prefer toform'with 3 1y from-the center. lhis tends to force the caster a pin receiving cavity which isdivided to form wheel against the central body member and the an upwardly extendingboss iii-and the lower pin side thrust is all taken at that point. This obreceiving socket l8 to permit both wheels viates one present deficiency of the usual casto just clear the swivel pin 12. This I have found ters in that they are given to wearing out the tobe a desirable arrangement in that a rea- 40 securing means disposed at the end of the axle. sonalcle amount of lubricant can be, placed in \Vith my present construction, if the caster is this socket no further lubricating need be not raised from the floor, it cannot come off applied for considerable period. About midway its sloping axle. The principal objects of my in this lower socket and disposed toward the present invention are: lower end of pin 12, I provide a lock pin 20. This 45 First. The provision of a caster unit which is disposed in a manner to go entirely thru the tracks much as a single caster wheel will track. cast m mber 14 and is adapted to engage-anan- .Second. A caster construction which admits nular groove 22cut in pin This folmsalockof having the greatest possible diameter in the ing means which makes itimpossibleforthe axle caster wheels for a given overall height. support member 14 to drop off the swivel pin. 50 Third. The provision or" a construction which Disposed at the center of frame 14 is the axle provides a very simple swiveling arrangement. shaft 24;; This may be formed preferably, as 'in- 7 Fourth. Acaster arrangement which provides dicated in the drawings, as part of the casting the maximum strength with the least amount 14. In some instances however it has .been foun-d of material. desirable to form axle 2s as a separate piece and 55 Other and more specific objects will be 'apparcast or otherwise secure it into casting .14.. In 11c any event it is desirable to have the two journals disposed at a small angle to each other so as to throw the wheels 26 and 30 at such an angle that they will meet at their lowermost point and be disposed suificiently far apart at their upper end to just provide clearance for the swivel pin 12.

At each end of the axle or journal proper as 33 and 34, I provide a wheel securing means. The most convenient form I have yet devised, is to provide a retaining washer 36 and then a split or cotterpin 38. This forms an inexpensive and secure fastening when it is borne in mind particularly that no end thrust ordinarily is placed upon pin 38.

Wheels 26 and 30 are formed most preferably with a spoke or web support center 40 which is disposed outwardly from the center of the wheel rim to the end that more space will be available inside the caster wheels for the supporting pin 12 and frame 14. In the various views I have shown a type of construction which has generally been applied to a caster having a wheel diameter of about 6 inches. In this form it is possible to have suificient material in frame 14 for the required strength without having the space inside the two wheels 26 and entirely filled with metal. To this end I have shown the substantially skeletonized form which is most clearly shown, possibly in Figures 2 and 7. To the end of having the bearing point as close to the junction of the two wheels as possible I have found it desirable to round the outer edge of the wheel rims as indicated at 31, substantially as shown in Figures 1, 4 and 8. This puts the point of greatest load near the inner edge of the rim of the two supporting wheels. In the drawings this feature has been somewhat exaggerated to bring it out most clearly.

In Figure 3 I have illustrated by the section line 8-8, the line marking the closest point the two wheels come together at their lowermost part and where they are spaced the widest apart at their upper extent. The purpose of having the two wheels touch together in front of their actual bearing, which would be directly under the axle as indicated by the other dashed line of Figure 3, is to give the camber action noted in automobile front wheels particularly. This gives a tendency for the two wheels to crowd inwardly or to track together as it were. In addition to this very desirable result it also prevents the picking up of small particles between the two wheels.

In Figure 4 I have indicated the lowermost point of the two wheels at 35 and 39 respectively. This places the point of bearing somewhat inside of the central plane of the wheel. The amount that this is inside of the central plane bears a direct relationship to the angularity of the axles. The action of the two thrusts is in an opposite sense. In other words, if the bearing point 39 were in the exact center of the wheel rim there would be a straight upward thrust. However, having it inside of the wheel central plane a triangle of force is produced which provides an outward thrust component-that is in the direction of the end of the axle toward the securing pin. Now the action of the slanting axle is to cause the wheels to go up the axle and an ideal condition obtained where these two forces equalize each other. In this case there would be no apparent side thrust either inwardly or outwardly. The two side thrusts, one outwardly and one inwardly being of such an extent as to counterbalance each other. This is a very desirable characteristic and one which must be proportioned for each design produced. In my drawings I have indicated a relationship which has been found to produce this result in this particular design. When this condition is maintained there is little wear and it is felt that this is a very desirable characteristic of my present construction. Shock loads caused by striking obstructions can be minimized by having the two wheels meet as at on line 88, under this condition at point of contact there is a rolling action in which the two wheels neutralize the thrust by a rolling thrust contact thereby having in effect all the desirable qualities of a single wheel caster.

Web 32 has been used as a filling piece to fill in the space which would normally be void between the two wheels at their upper edges. This provides a higher degree of finish and also prevents large objects, gravel and the like, getting in between the two wheels at a point where they are well spaced apart and then locking as they drop to the lower portions where the wheels are quite close together. It should be quite apparent that the metal at the left of axle 24 as viewed in Figure 2 is normally not needed for strength. There are occasions however when it does serve a useful purpose. This condition arises when thru some unforeseen contingency the caster wheels are pulled sideways, this would place a heavy strain on the axles themselves were it not for rim 32. As disposed, however, rim 32 forms a support or stop which limits the inward movement of the wheels and often prevents serious damage either to the wheels themselves or to the journals 33 and 34.

It is desired to invite attention to the fact that socket 18 is disposed considerably to one side of axle 24. The amount of this displacement is determined by the degree of caster action desired. Attention is further invited to the fact that the wheels themselves, under the construction shown, can extend upwardly so they just clear base 10. This permits having wheels of the maximum diameter, for a given overall height, a very desirable characteristic of my construction.

The foregoing description and the accompanying drawings are believed to clearly disclose a preferred embodiment of my invention but it will be understood that this disclosure is merely illustrative and that such changes in the invention as may be made are fairly within the scope and spirit of the following claims.

Having thus fully described my invention, what I claim as new and desire to secure by Letters Patent is:-

l. The combination in a duplex caster with a base and a rigid swivel pin, of a wheel frame having a socket for said pin, laterally extending declining axles on said frame, and-a pair of oppositely cambered wheels on said axles which engage each other in rolling contact at a point slightly in front of said axles.

2. In a duplex caster the combination with a pair of oppositely cambered wheels, the rims of the wheels having lateral contact with each other in front of their lowermost points, said rims having transversely rounded treads, and the maximum peripheries of the treads being located adjacent the lateral contact points.

3. The combination with a base plate and rigid tapering swivel pin, of an arcuate shaped wheel frame having a socket for said pin and means for securing the pin in the socket, a bearing boss rigid with the frame and spaced from the socket,

a pair of laterally extending declining axles on the frame, and a pair of cambered wheels journaled on said axles which engage each other in rolling contact at a point slightly in front of said axles.

4. In a duplex caster the combination with a wheel supporting frame; a pair of oppositely cambered wheels, the rims of said wheels having lateral contact with each other in front of 

